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Extension > Garden > Diagnose a problem > What's wrong with my plant? > Vegetable > Potato > Flecks, spots, streaks, or blotches on leaves

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Potato > Leaves > Flecks, spots, streaks, or blotches on leaves

1 of 6
  • Early Blight 1
  • Early Blight 2
  • Early Blight 3

Early Blight
Alternaria solani

  • Leaf spots are round, brown with target like rings inside
  • When severe many leaf spots grow together resulting in large brown patches and leaves turn yellow
  • Stem lesions are dark, slightly sunken areas
  • Potato tubers develop dark, sunken spots surrounded by a purplish brown raised border
  • Rough, corky dry tissue can be seen below tuber spots when cut open
  • More prevalent in warm and humid weather
  • More information on Early Blight...
2 of 6
  • Late Blight 1
  • Late Blight 2
  • Late Blight 3

Late Blight
Phytophthora infestans

  • Large irregular olive to brown leaf spots that are not restricted by leaf veins
  • In wet weather, leaves, stems and petioles rapidly turn brown and shrivel
  • Powdery white fungal growth can be seen on infected tissue in wet weather
  • Irregular sunken, dull brown to purple lesions around the eyes on potato tubers
  • Inside of potato tuber has a reddish-brown dry rot
  • More prevalent in years of cool and wet weather
  • More information on Late Blight...
3 of 6
  • Verticillium Wilt 1
  • Verticillium Wilt 2
  • Verticillium Wilt 3

Verticillium Wilt
Verticillium spp.

  • Leaves turn yellow then brown and wilted, stems remain erect
  • Symptoms are often seen on one or a few stems but not the entire plant
  • Often only random plants scattered in the field are affected
  • If the stem is cut near the soil line, brown streaks or rings can be seen just under the skin
  • Dark brown to black streaks or rings can be seen in the tuber flesh if cut on the stem end
  • More information on Verticillium Wilt...
4 of 6
  • Corky Ring Spot 1
  • Corky Ring Spot 2
  • Corky Ring Spot 3

Corky Ring Spot
Tobacco Rattle Virus

  • Leaves may have no symptoms or have yellow rings, spots and arcs
  • Stems may be mottled green and yellow
  • Brown rings and arcs form on the skin and in the flesh of tubers
  • Potato tubers can be cracked and malformed if infections comes in early
  • More information on Corky Ring Spot...
5 of 6
  • Potato Virus Y 1
  • Potato Virus Y 2

Potato Virus Y (PVY)

  • Leaf symptoms vary greatly depending on strain of virus present
  • Light and dark green mosaic pattern on leaves, occasionally leaves crinkle
  • In severe cases, light brown rings form on tuber skin
  • More information on Potato Virus Y (PVY)...
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  • Black Dot 1
  • Black Dot 2
  • Black Dot 3

Black Dot
Colletotrichum coccodes

  • Leaves may have random brown spots, or may yellow and wilt due to infection of stem and roots
  • Irregular patches of gray discoloration on surface of the potato tuber
  • Sunken dark brown to black lesion on stem that turns white in the center with age
  • Many pinprick sized black dots can be seen on infected stems and tubers (handlens is helpful)
  • More information on Black Dot...

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